Can You Exercise While Doing A 36 Hour Fast - Keto Made Simple for 40 and Over

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Going for a 36-hour fast is a pretty bold choice, and one question that pops up a lot is whether it’s smart—or even safe—to exercise during such a long fasting window. I hear this from folks looking to amp up fat loss or see if training on an empty tank brings some kind of edge. I’ll break down the basics, look at what happens in the body, and share tips to help you make your own call about workouts while fasting.

A minimalist kitchen countertop with a water bottle and dumbbells, bathed in early morning light, evoking stillness and a focus on wellness.

What Happens in Your Body During a 36-Hour Fast?

Fasting for 36 hours means going a day and a half with no calories—just water, black coffee, or unsweetened tea for most people. When you get into these longer fasts, your body starts to switch gears completely. Here’s the basic rundown:

Glycogen Runs Low: By 24 hours, your body has mostly burned through glycogen, the stored form of carbs in your muscles and liver.
Fat Burning Ramps Up: Without steady carbs, your body taps into fat stores for energy, producing ketones that fuel your brain and body.
Blood Sugar Drops: Your blood sugar gets pretty stable, but some people notice feeling weaker or more tired.
Hormones Change: Fasting increases growth hormone and norepinephrine, which can actually help preserve muscle and might help with fat burning.

I notice a pretty clear mental switch up when I’ve gone over 24 hours fasting. My thinking gets sharp, but my energy for tough workouts definitely dips. These adaptations are normal, but your body is basically in energy conservation mode.

Is It Safe to Exercise While Doing a 36-Hour Fast?

There’s not a simple yes or no here, but most healthy people can do light to moderate exercise during a 36-hour fast and feel fine. The big thing is listening to your body and knowing your limits. Exercise puts extra stress on the system, especially when fuel levels are super low.

Research on short fasts (under 48 hours) suggests that as long as you’re staying hydrated and not pushing elite level intensity, there’s generally not a huge risk for healthy adults. However, if you have any underlying health issues, including diabetes, heart conditions, or take meds that affect blood sugar, it’s really important to check with your doctor first.

Low Intensity Cardio: A gentle walk, slow bike ride, or easy yoga usually feels okay and can even help with the mood swings or restlessness some people get during longer fasts.
Strength Training: Lifting weights or doing bodyweight exercises is possible, but you may notice you can’t lift as heavy, or you run out of steam a lot quicker. I find it pretty tough to hit my regular numbers if I’m deep into a fast.

It’s super important to avoid high-risk workouts (like heavy HIIT circuits or long endurance runs) if you haven’t done this before. Dizziness, cramping, and sudden fatigue can sneak up fast during a long fast.

Tips for Exercising During a 36-Hour Fast

If you do want to keep moving while fasting, here are the main things that work for me and others who mix fasting and fitness:

Ease Into It: Try a gentle walk, stretching, or a short bodyweight routine first. See how your body reacts before trying anything tougher.
Stay Hydrated: Water is nonnegotiable. Dehydration hits hard during a long fast and makes any kind of activity feel ten times tougher. I keep a bottle of water close by at all times, especially if I’m sweating.
Watch for Warning Signs: Stop right away if you get dizzy, confused, lightheaded, or nauseous. Rest, sip water, and don’t power through it.
Avoid Intense Training: Save sprints, max lifts, and longdistance stuff for eating days. Mild to moderate movement works better.
Plan Your Workouts: If you’re used to morning workouts, it’s sometimes easier to exercise at the start of your fast, before energy dips. Some folks save their movement for the end, right before breaking the fast, so they don’t stay hungry afterwards.

I usually feel better sticking to slower, mindful movement like light walking or easy routines if I’m midway through a fast, but your experience can be different. Over time, tracking your results in a workout journal or even using a fitness app can help you spot patterns and learn what movements your body handles best while fasting. Other factors—like temperature, stress levels, and how well you slept before the fast—also make a difference. Pay attention to these variables, and you’ll be able to tailor your workouts more effectively.

Benefits and Drawbacks of Exercising While Fasting

There are a few reasons people choose to move while fasting, and some solid downsides to keep in mind too.

Potential Benefits

Increased Fat Burning: Without food coming in, your body relies even more on stored fat for fuel.
Mental Boost: Exercise tends to improve mood and reduce anxiety, which sometimes spikes during longer fasts. Even a walk clears my head after 24 hours without food.
Improved Insulin Sensitivity: Movement plus fasting may improve how your body handles carbs when you eat again.
Heightened Mindfulness: Training while fasting can make you more aware of your body’s signals, helping you build a more intuitive approach to fitness and nutrition over time.

Drawbacks and Risks

Reduced Strength and Stamina: Most people notice their lifts, sprints, or endurance dip a lot while fasting this long. I lose some pep even on regular 16hour fasts, so 36 definitely makes it tricky to train hard.
Low Blood Sugar: Signs like feeling shaky, dizzy, or getting a headache are worth watching out for, especially on hot days or if you’re doing more than gentle movement.
Muscle Breakdown: Fasting increases growth hormone, but if you push too hard on no fuel, the body sometimes breaks down muscle for energy, especially if you’re already lean.
Attention to Recovery: With less energy available, muscles may take longer to recover post-exercise, increasing the importance of rest and good nutrition after your fasting window.

Things to Consider Before Working Out on a Fast

Mixing fasting with fitness isn’t for everyone, so a bit of planning goes a long way. Here are a few things worth considering before stepping into a 36-hour fast and move experiment:

Your Starting Point: If you’re new to fasting or exercise, try one at a time—not both together. Your body needs time to adjust.
Hydration and Electrolytes: Not eating means no sodium, potassium, magnesium, or other minerals you usually get from food. I sometimes add electrolyte tablets to my water to help avoid cramps or headaches.
Current Health: If you have any chronic medical conditions, are underweight, or prone to low blood sugar, talk to a healthcare provider first.
Sleep and Recovery: Fasting can make sleep a little weird and recovery slower, especially if you’re moving a lot or not used to it.
Support Networks: Having a friend or workout buddy to check in with during your fasting days can provide motivation and help keep you accountable, especially if you start feeling off.
Honest SelfAssessment: Take a minute for some honest reflection: Are you fasting for the right reasons? Checking in with your own habits and body cues will make it more likely you’ll have a positive experience.

Personal Experience: Testing Movement While Fasting

The first time I tried mixing exercise with a fast longer than a day, I was surprised by how much my routine switched up. I could still walk or do some stretching, but runs or hard lifting just felt flat. The best results came from focusing on slow, low-stress movement and waiting until after refeeding to do anything extreme. Other people I know, especially those who are used to long intermittent fasts, sometimes sneak in regular workouts with no problem, but almost everyone adjusts the volume and intensity way down. Tuning into your own experience and making small adjustments each fast helps set a practical routine that won’t drain your reserves too quickly.

Real-World Examples and Everyday Applications

Some athletes and fitness fans, especially those following intermittent fasting or training for events, include fasted workouts in their regular routines. There are stories of runners doing easy miles toward the end of a fast, or yoga fans saying they prefer deep stretching when their stomach is empty. However, these routines are usually built up with practice and aren’t something I’d jump into without some trial runs. It’s also common to tie fasted movement to specific goals, like improving metabolic flexibility or making workouts fit a busy schedule where big meals aren’t always convenient. Just remember, what feels right for one person might not line up for someone else.

Walking: Works really well for most people and carries a low risk, even deep into a fast.
Gentle Yoga or Bodyweight Routines: Great for flexibility, breathwork, and movement without major energy drain.
Skipping Intense Cardio or Lifting: Science and experience both lean toward easing off the gas for heavy lifting or interval training if you haven’t eaten in 24 hours or more.

Frequently Asked Questions

Here are answers to questions I often get about working out during a longer fast:

Can fasting and exercise help with fat loss?
Answer: Pairing movement and fasting can increase fat burning for some people, but don’t expect huge boosts over the long term. It mostly comes down to consistency and not overeating when you break the fast.

Is muscle loss a big worry during a 36-hour fast?
Answer: For most people, short fasts like 36 hours don’t cause much muscle loss, but pushing really hard with zero fuel can tip your body into breaking down some muscle tissue, especially if you do it often or are already super lean.

What about hydration—do I need electrolytes?
Answer: If you’re just drinking water for 36 hours and sweating or peeing a lot, you might need some extra salt or magnesium. There are lots of low-calorie electrolyte options available, worth checking out if you get headaches, cramps, or feel foggy.

Moving Forward: Finding Your Balance

Exercising during a 36-hour fast can work for some people, especially with low intensity movement and plenty of hydration. Listening to your body, starting slow, and paying attention to how you feel is really important. Everyone’s different and what works for one person might not for another. If you’re new to fasting or exercise, building up gradually and keeping things flexible helps you avoid the rough patches and get more benefits out of both fasting and movement.

Curious about how your body responds? Start light, keep it simple, and enjoy the unique challenge. It’s definitely a learning experience worth exploring if you’re feeling up for it. Remember to track your progress, notice how you feel, and readjust as needed for future fasts or fitness adventures.